By Your Side
by b.k.b.28
Summary: Always AU: Kate can't stop thinking about Castle; their fight, how she let him go. How she almost died. Then she realises that Maddox may not be finished and he's his next victim.
1. Let Him Go

_You let him go._

That thought rings on a continuous loop in Kate Beckett's head, taunting her. It screams at her above the torrent of rain that descends, thoroughly soaking her clothes and hair. It drowns out the conversation that surrounds her.

"Detective!"

_She let him go._

"Detective Beckett!"

Kate snaps out of her trance, her vacant eyes searching for the source. They land on Captain Gates.

"Nice to see you're back on Earth, Detective," Gates remarks wryly, causing Beckett to blush. "Detective Ryan will transport you back and Detective Esposito, you will come with me."

Esposito groans a little more audibly than intended, glaring at Ryan who rolls his eyes in response. "Of course; it's _my_ fault!" Ryan hisses as his partner climbs into the car, purposely slamming the door after him.

Drama_ Queens._

"Ryan, I trust that you and Detective Beckett aren't planning on running off?" Captain Gates queries.

"No, Sir."

"Well then, we shall meet you back at the precinct," are their Captain's last words as she disappears inside her car.

* * *

Once again, Beckett is withdrawn; her eyes on the droplets of rain that run down the car window and her mind on the same thought that has been provoking her for a while.

"I let him go," she blurts out, shocked that she'd said it aloud.

"Beckett, you were hanging off the edge of a rooftop! Of course you did."

"No...I don't mean Maddox."

Ryan frowns. "Who then?" Ryan realises he is asking the obvious immediately after he finishes. "Castle."

"He was right. And I wouldn't listen." Kate tries to hold back tears. She can feel it now. Her wall is crumbling, gradually _tumbling_ at her feet. She _loves_ him. She needs him. She wants him.

"We'll find Maddox," Ryan uncomfortably changes the subject. "Somehow."

She laughs cynically. "He doesn't want to be found. Said that if I die, I'd die knowing that I'd let him go. But if I live, he would have to die."

_I let him go._

Ryan smiles for the first time all evening. "Beckett, that's good! You live. He dies."

_She let him go. She lives_._ He dies_.

Beckett's face whitens.

"Beckett?"

Maddox wasn't talking about himself.

_She lives. He dies._

"Kate, are you okay?"

_Oh no!_

"Castle!" she gasps.

"Kate? What about him?"

"I live. He dies; except he didn't mean _himself_. He meant Castle."

Ryan's eyes widen. "He must have seen us rescue you. That's when he ran. He knows that you're alive!"

"And he's going to kill Castle!"


	2. Sorry Isn't Good Enough

_"I'll be by your side, wherever you fall,_

_In the dead of night, whenever you call,_

_And please don't fight, these hand that are holding you."_

_\- By Your Side: Tenth Avenue North_

* * *

"Ryan, turn the car around!" Kate demands, her heart pounding in her chest.

"Shouldn't we tell Gates-"

"Ryan!" She snaps, but it isn't out of anger; there is desperation in her voice.

"Yeah...sorry. Castle is more important than my job," he acquiesces. He abruptly swerves the car around, tyres screeching beneath them. Kate fishes her phone out, her fingers rapidly tapping against the touch screen.

"Who are you calling?"

"Who do you think?" She replies, a little more sanctimonious than she meant to be.

"Right..." Ryan feels moronic. "Do you think he'll pick up?"

"I highly doubt it."

"Whatever happens, he'll come back. He always does."

"This time... I'm really not sure," Beckett sighs, pressing the phone to her ear.

_Please_ _Castle. Please pick up._

_"This is Richard Castle. I can't take your call right now but please leave a message and I'll get back to you as soon as possible."_

She screws her eyes shut in defeat, about to hang up when she hears the tone. She has to leave a message.

"Rick," she breathes into the phone. "You _know_ who this is. And I know you think that this is some kind of plea for forgiveness- and frankly if I weren't in this situation it would be- but there isn't time for that." She takes a deep breath before continuing, attempting to swallow the lump in her throat.

"You were right. Maddox tried to kill me. Left me to hang off the edge of a rooftop and if it weren't for Kev, I'd be dead." She shoots him a grateful smile and he returns one.

"But we think he's after you now, because he knows that I lived; and if he can't kill me himself he will have to punish me in some way. Make my life torture and trust me Castle when I say that if you die, I am just as good as dead too."

It only dawned on her what she had said, moments afterwards but it felt good. A relief even. She had pretty much just confessed her love for him, even if he didn't hear it.

"Rick, please. Just...listen. If you hear this, run. Run as fast as you can, as far as you can. Be inconspicuous, but most importantly be safe." She has an idea. "Go to my apartment. My spare key is under the doormat. Lock the door. Lock the windows. Don't let anyone inside unless you are sure that it is me. I'll be there. I'll find you. And I'm sorry. I know it isn't enough but...I'm sorry."

She hangs up, wiping tears that she hadn't even known were there. She can't lose him. Not now. Not after everything that they've been through. Four years. It can't end like this.

"So, your apartment?" Kevin asks softly.

"My apartment," Kate confirms.

"And what if he isn't there?"

"He has to be. Otherwise...I'm not sure that we can save him in time."

"Should we call Gates? Get backup?"

"Not yet. Not until I know Castle is safe. We don't want to risk her chasing after us. You don't need to be punished as well. It was Espo and I who were idiotic enough to hurl ourselves into Maddox's hands."

"Hey, I'm your partner. I'm happy to take some of the blame and honestly, considering we are currently entirely disobeying our captain's orders, I am unlikely to be let off lightly."

"I'm sorry that I got you all into this mess."

"Don't be. I'd regret if if I didn't help you anyway."

"Thanks, Kev. I needed to hear that."

"Anytime," he smiles and although he didn't have a clue, Kate couldn't help but associate it to what Castle would always tell her.

_Always._

Now it seems that their always is in fact a very short amount of time. Four years is nothing compared to an eternity. He broke their promise. They both did.

* * *

The moment they arrive, Beckett scrambles out of her car, fumbling for her keys. Simultaneously, she dials Esposito's number.

"Beckett, where the hell are you? Gates is gonna kill you if you don't get here soon!"

"Espo, I'm giving you to Ryan. He'll explain everything."

"I am NOT speaking to him!" He protests.

"Beckett-" Ryan begins.

"Stop it! Both of you!" She snaps for the second time today, causing both men to fall silent with guilt. "My partner is either in there..." She points to her apartment; "Or he is at home. And if he is at home, then the chances of him being alive are so little to nothing that I don't even want to think about that option right now! So you two can continue to argue like a couple of four year olds, or you can at least _try_ to help me save the man I love!"

Ryan watches, dumbfounded as tears stream controllably out of her aflame eyes. Beckett shoves the phone into his frozen hand and storms into her apartment without looking back.

They're grown men. They can solve their own issues.

All the lights are off. Either that is a tactful desicion from Castle or they haven't been switched on since she was last there. "Castle!" She calls. "Rick! It's me. You're safe now. I'm here."

No reply. Her breathing quickens as a wave of dread sweeps over her. "Rick?"

He has to be here. He _has_ to be.

"Please. Castle. Please."

Her knees begin to buckle and her body weakens as she realises that he didn't pick up her message. That man. Why does he have to be so stubborn? Her back slides down the wall, her eyes blinded by tears; the sound that escapes her mouth surprises even herself.

"Beckett?" Ryan's concerned voice calls down the hallway. When he appears, he is still on the phone to Esposito. "He isn't here, is he?"

Beckett shakes her head, taking Kevin's free hand as he pulls her onto her feet.

"Put the phone on speaker," she whimpers. "Javi?"

"What do you want me to do, Beckett?"

"Tell Gates everything. Get backup and drive down to Castle's."

"And if Gates says no?" asks Ryan.

"I'll go anyway," Javier replies.

"And us?"

"We'll go there too," says Beckett.

"Okay. I'll call you," says Espo before he ends the call.

Kate takes her phone and slips it into her pocket, distant.

"Kate?"

"It's all my fault. He's probably dead because of me. If I had just-"

"Shh, no!" It's his go to scold her back. "Don't ever blame yourself. I've made that mistake plenty of times." He places his hands on her shoulders and stares intensely into her eyes. "You aren't the killer. It wasn't your decision for any of this to happen. He chose to kill you. To kill him. But you don't have the time to blame yourself as it is Maddox to blame. Now, we need to at least try to get to Castle before it's too late. Okay?"

Kate nods obediently. She follows Ryan and then halts at the door. There is a USB stick on the floor with a note attached. She picks it up.

"Beckett, 'you coming?"

"I'm just getting something!" She disappears into her room. When she returns she is reading the note, attempting the uncover its meaning.

_In case you change your mind. You need to know this._

_R.C._

* * *

**A.N: The response to this story has been incredible! Thank-you! The next chapter will be posted soon. What Beckett went to get will eventually become clear and also the meaning of the note and USB. Sorry for the short chapters; it's only so there will be more in the story as it isn't particularly long.**

**Thanks so much for reading!**

**\- B xx**


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